The present invention relates to a head positioning system for magnetic disk drives, which drives a magnetic head from a current track to a target in the radial direction of a magnetic disk and then positions the magnetic head on the center line of the target track.
Such a head positioning system is required to correct a magnetic head position such that the magnetic head is accurately located on the center line of the target track after a track seeking operation is completed due to dimensional deviations in the magnetic disk because of temperature and humidity changes. To this end, the conventional head positioning system utilizes servo information recorded on a part of a data surface of the magnetic disk as disclosed in U.S. Pat. No. 4,122,503. In the system, the magnetic disk includes an inner servo track x.sub.0 and an outer servo track x.sub.1 on which the servo information is prerecorded. The head positioning system initially positions the magnetic head at the inner and outer servo track and then reads the servo information by means of the magnetic head to obtain deviation values y.sub.0 and y.sub.1 of the head with respect to the inner and outer servo tracks x.sub.0 and x.sub.1, respectively. When the head positioning system positions the magnetic head at a target data track n which is located between the inner and outer servo tracks x.sub.0 and x.sub.1, an offset correction value y, which represents a deviation of the magnetic head from the center line of the target track n after the track seeking operation, is calculated as follows: ##EQU1## That is, the correction value y is estimated in accordance with an assumption that the deviation of the magnetic head on the target track n increases or decreases in proportion to the radial position of the target track n.
However, the inventors of the present invention have found that the actual deviation of the magnetic head is not accurately represented by the above formula since the head positioning system consists of various components which have various thermal expansion coefficients. Accordingly, in the conventional head positioning system, the deviation of the magnetic head from the center line of the target track is still relatively large so that the track width of the magnetic disk is made inevitably wide enough to render negligible the deviation of the magnetic head. Thus, the high track density cannot be realized.